1. Field of the Invention
The present invention relates to a master cylinder for supplying a brake fluid to a brake apparatus of an automobile or the like.
2. Description of the Related Art
As a conventional master cylinder, as described in a microfilm of A Japanese Utility Model Application No. 152602/1980 (Japanese Utility Model Laid-Open No. 73248/1982), there is provided a constitution in which by carrying out so-to-speak fast fill for supplying a large volume of a brake fluid at an initial stage of operation when the brake fluid is supplied to a brake apparatus such as a disk brake or a drum brake, an ineffective fluid amount at an initial stage of stroke is compensated for, and as a result, a pedal stroke can be shortened (fast fill type master cylinder).
The fast fill type master cylinder is provided with a stepped cylinder having a large diameter cylinder portion and a small diameter cylinder portion, a stepped piston having a large diameter piston portion slidably inserted into the large diameter cylinder portion of the stepped cylinder and a small diameter piston portion slidably inserted into the small diameter cylinder portion of the stepped cylinder, and a cup seal (reverse flow checking opening and closing portion) for partitioning the inside of the stepped cylinder into a large diameter pressurizing chamber on the large diameter piston portion side and a small diameter hydraulic chamber on the small diameter piston portion side and permitting the brake fluid flow only from the large diameter pressurizing chamber side to the small diameter hydraulic chamber side.
Further, when the stepped piston is slidingly moved toward the small diameter hydraulic chamber by an input from a brake pedal, a volume of the large diameter pressurizing chamber is reduced by the sliding movement of the stepped piston, so that the reverse flow checking opening and closing portion is opened to supply the fluid from the large diameter pressurizing chamber side to the small diameter hydraulic chamber side the above-described fast fill, which carries out.
Further, the fast fill type master cylinder is provided with a relief valve for escaping the brake fluid from the large diameter pressurizing chamber to a reservoir when an inner pressure of the large diameter pressurizing chamber becomes equal to or higher than a predetermined value, and a notch is provided at the relief valve to always communicate the large diameter pressurizing chamber to the reservoir. Through the communication path of an extremely small diameter due to the notch, the fluid is supplied from the reservoir to the large diameter pressurizing chamber.
Meanwhile, there poses a problem that since the above-described master cylinder is provided with the notch, when the pressure is elevated slowly, the fluid of the large diameter pressurizing chamber flows to the reservoir and the fast fill cannot be carried out sufficiently.
Further, according to the above-described master cylinder, when the inner pressure of the large diameter pressurizing chamber becomes equal to or higher than the predetermined value, the relief valve is opened and the brake fluid is quickly escaped from the large diameter pressuring chamber to the reservoir. Therefore, when the pressure is elevated at high rate, namely when in operation of the brake pedal is stepped at comparatively fast, the hydraulic pressure of the large diameter pressurizing chamber is quickly released by the opening operation of the relief valve when hydraulic pressure of the large diameter pressurizing chamber is elevated to the predetermined pressure and therefore, a pedal stroke is extended without being accompanied by pedal reaction force and the piston is moved to the small diameter hydraulic chamber side. This has brought about a strange feeling in the pedal operation that the vehicle speed is reduced without a real feeling that the pedal is depressed.
Further, there is another conventional fast fill type master cylinder having a cut-off portion on the large diameter pressurizing chamber side for cutting communication between the large diameter pressurizing chamber and the reservoir by being closed by the sliding movement to the small diameter hydraulic chamber side of the stepped piston and a cut-off portion on the small diameter hydraulic chamber side for cutting communication between the large diameter pressurizing chamber and the small diameter hydraulic chamber by being closed by the sliding movement to the small diameter hydraulic chamber side of the stepped piston in order to promote the fast fill function. In order to promote the fast fill function in such a master cylinder, it is necessary to make an ineffective stroke of the stepped piston until the cut-off portion on the small diameter hydraulic chamber side and the cut-off portion on the large diameter pressurizing chamber side are brought into a closed state, as short as possible.
However, when the ineffective stroke is simply set to be short, sectional areas of flow paths of the cut-off portion on the side of the small diameter hydraulic chamber and the cut-off portion on the side of the large diameter pressurizing chamber, are narrowed. When the sectional areas of the flow paths are narrowed in this way, in the case that the master cylinder is used in a combination with a traction control apparatus, there poses a problem that when the brake fluid is forcibly sucked from the reservoir via the master cylinder in order to make the traction control apparatus operate the brake apparatus, the brake fluid cannot be made to flow at a sufficient flow rate, that is, in high flow.
It is noted that the traction control apparatus is an apparatus that, when the brake pedal is not operated, a driver excessively operates an accelerator on a slippery road and causes a wheel spin at a drive wheel of a vehicle, controls the drive wheel by forcibly supplying the brake fluid from the reservoir to a brake apparatus such as a wheel cylinder via the master cylinder, thereby to reduce the wheel spin. The master cylinder used in the combination with the traction control apparatus must have a function capable of making the brake fluid flow to the traction control apparatus in high flow (high flow function) in an initial state.
Therefore, the applicant has conceived that a structure of previously filed Japanese Patent Application No. 294502/1998 (equivalent to U.S. Pat. No. 6,272,858 B1) to the cut-off portion on the small diameter hydraulic chamber side and the cut-off portion on the large diameter pressurizing chamber side. The structure is to close a port opened at an outer peripheral portion of the piston by a cup seal by the sliding movement of the piston. By forming a control taper face, a front side of which is smaller in diameter, rearward from the opening portion of the port at the outer peripheral portion of the piston, even when the entire of the cup seal does not completely pass over the port in the sliding movement of the piston, a rear end portion of the cup seal rides over the control taper face to thereby increase face pressure and close the port. The structure can shorten the ineffective stroke of the piston while achieving the high flow.
However, when the above-described structure is applied to the cut-off portion on the small diameter hydraulic chamber side and the cut-off portion on the large diameter pressurizing chamber side, the control taper face are required in both of the cut-off portions, further, it is necessary to strictly control positional accuracy of both of the ports and therefore, there poses a problem that cost is increased.
The present invention has been made in view of the above-described situation and it is an object thereof to provide a master cylinder capable of reducing a strange feeling in a pedal operation brought when a hydraulic pressure of a large diameter pressurizing chamber is released while ensuring a fast fill function.
Further, it is another object of the invention to provide a master cylinder capable of shortening a pedal stroke while satisfying a high flow function needed in combining the master cylinder with a traction control apparatus and capable of reducing cost.
In order to achieve the above-described objects, according to an aspect of the invention, there is provided a master cylinder comprising a stepped cylinder having a large diameter cylinder portion and a small diameter cylinder portion; a stepped piston having a large diameter piston portion slidably inserted into the large diameter cylinder portion of the stepped cylinder and a small diameter piston portion slidably inserted into the small diameter cylinder portion of the stepped cylinder; and a reverse flow checking opening and closing portion for partitioning the inside of the stepped cylinder into a large diameter pressurizing chamber on the large diameter piston portion side and a small diameter hydraulic chamber on the small diameter piston portion side and permitting a brake fluid to flow only from the large diameter pressurizing chamber side to the small diameter hydraulic chamber side, the reverse flow checking opening and closing portion being opened by reducing a volume of the large diameter pressurizing chamber by sliding movement of the stepped piston toward the small diameter hydraulic chamber side to thereby supply the brake fluid from the large diameter pressurizing chamber side to the small diameter hydraulic chamber side, wherein the master cylinder is provided with a control valve for gradually reducing a hydraulic pressure of the large diameter pressurizing chamber in accordance with the rise of the hydraulic pressure of the small diameter hydraulic chamber.
Further, the master cylinder may be constructed such that the control valve includes a valve piston and a valve spring for urging the valve piston within a valve cylinder; and the valve piston reduces the hydraulic pressure of the large diameter pressurizing chamber when a total force of a propulsive force produced by the hydraulic pressure of the small diameter hydraulic chamber and a propulsive force produced by the hydraulic pressure of the large diameter pressurizing chamber exceeds an urge force by the valve spring.
Further, the master cylinder may be constructed such that it includes a reservoir for storing the brake fluid; the control valve is provided with at least two ring seals between the valve cylinder and the valve piston to partition the inside of the valve cylinder, and a chamber formed between the ring seals and the small diameter hydraulic chamber communicate with each other; and the valve spring is provided at one end side of the valve piston, and a relief chamber for communicating to the reservoir and the large diameter pressurizing chamber is provided at the other end side of the valve piston, with an opening and closing valve mechanism for communicating and cutting between the relief chamber and the large diameter pressurizing chamber being provided. Further, the master cylinder may be constructed such that the at least two ring seals are provided at the valve piston, and the diameter of the ring seal provided on the valve spring side is larger than that of the ring seal provided on the relief chamber side.
In this way, since there is provided the control valve capable of escaping the hydraulic pressure of the large diameter pressurizing chamber to the reservoir side to gradually lower it in accordance with the rise of the hydraulic pressure of the small diameter hydraulic chamber, the brake fluid is supplied from the large diameter pressurizing chamber side to the small diameter hydraulic chamber side by the opening operation of the reverse flow checking opening and closing portion by reducing the volume of the large diameter pressurizing chamber by the sliding movement of the stepped piston to the small diameter hydraulic chamber side, that is, fast fill, and when the liquid pressure of the large diameter pressurizing chamber rises, the control valve escapes the hydraulic pressure of the large diameter pressurizing chamber to the reservoir to gradually lower it in accordance with the rise of the hydraulic pressure of the small diameter hydraulic chamber. Therefore, a pedal stroke can be shortened by the effect of the fast fill, and when the hydraulic pressure of the large diameter pressurizing chamber is released, the hydraulic pressure of the large diameter pressurizing chamber is not quickly lowered but is lowered gradually.
Further, the at least two ring seals are provided at the valve piston, and the diameter of the ring seal provided on the valve spring side is larger than that of the ring seal provided on the relief chamber side. Therefore, the valve piston can be urged by the hydraulic pressure worked inside the chamber formed between the ring seals, whereby the opening and closing valve mechanism can be driven.
In addition, the master cylinder may be constructed such that the valve cylinder is partitioned into three chambers, that is, the relief chamber, the chamber formed between the ring seals and a damper chamber which stores the valve spring, by the two ring seals, and the valve piston is formed with a throttle path one end side of which is opened to the relief chamber and the other end side of which is opened to the damper chamber.
Thus, since the damper chamber and the relief chamber are communicated to each other via the throttle path, when the valve piston of the opening and closing valve mechanism finely vibrates at high speed in escaping the hydraulic pressure of the large diameter pressurizing chamber to the reservoir side to gradually lower it in accordance with the rise of the hydraulic pressure of the small diameter hydraulic chamber, the volume of the damper chamber repeatedly increases and reduces finely. As a result, the brake fluid is reciprocated between the damper chamber and the relief chamber via the throttle path, and the damper effect is achieved by constituting fluid flow resistance by the throttle path.
In addition, the master cylinder may be constructed such that it further comprises a reservoir for storing the brake fluid; a cut-off portion on the large diameter pressurizing chamber side for cutting communication between the large diameter pressurizing chamber and the reservoir by being closed by the sliding movement of the stepped piston to the small diameter hydraulic chamber side; and a cut-off portion on the small diameter hydraulic chamber side for cutting communication between the large diameter pressurizing chamber and the small diameter hydraulic chamber by being closed by the sliding movement of the stepped piston to the small diameter hydraulic chamber side, wherein an ineffective stroke of the stepped piston until the cut-off portion on the small diameter hydraulic chamber side is brought into a closed state is made longer than an ineffective stroke of the stepped piston until the cut-off portion on the large diameter pressurizing chamber side is brought into a closed state.
Further, according to another aspect of the invention, there is provided a master cylinder comprising a stepped cylinder having a large diameter cylinder portion and a small diameter cylinder portion; a stepped piston having a large diameter piston portion slidably inserted into the large diameter cylinder portion of the stepped cylinder and a small diameter piston portion slidably inserted into the small cylinder portion of the stepped cylinder; a reverse flow checking opening and closing portion for partitioning the inside of the stepped cylinder into a large diameter pressurizing chamber on the large diameter piston portion side and a small diameter hydraulic chamber on the small diameter piston portion side and permitting a brake fluid to flow only from the large diameter pressurizing chamber side to the small diameter hydraulic chamber; a cut-off portion on the large diameter pressurizing chamber side for cutting communication between the large diameter pressurizing chamber and a reservoir by being closed by sliding movement of the stepped piston to the small diameter hydraulic chamber; and a cut-off portion on the small diameter hydraulic chamber side for cutting communication between the large diameter pressurizing chamber and the small diameter hydraulic chamber by being closed by the sliding movement of the stepped piston to the small diameter hydraulic chamber side, the brake fluid being supplied from the large diameter pressurizing chamber side to the small diameter hydraulic chamber side by the opening operation of the reverse flow checking opening and closing portion by reducing a volume of the large diameter pressurizing chamber by the sliding movement of the stepped piston to the small diameter hydraulic chamber side, wherein an ineffective stroke of the stepped piston until the cut-off portion on the small diameter hydraulic chamber side is brought into the closed state is made longer than an ineffective stroke of the stepped piston until the cut-off portion on the large diameter pressurizing chamber side is brought into a closed state.
When constituted in this way, in supplying the brake fluid from the large diameter pressurizing chamber to the small diameter hydraulic chamber, even when the cut-off portion on the small diameter hydraulic chamber side having the longer ineffective stroke is not brought into the closed state, so far as the cut-off portion on the large diameter pressurizing chamber side having the shorter ineffective stroke is brought into the closed state, the brake fluid flow caused by reducing the volume of the large diameter pressurizing chamber by the sliding movement of the stepped piston toward the small diameter hydraulic chamber, via the cut-off portion on the small diameter hydraulic chamber side, is from the large diameter pressurizing chamber side to the small diameter hydraulic chamber side and the same as that in supplying the fluid from the large diameter pressurizing chamber side to the small diameter hydraulic chamber side via the reverse flow checking opening and closing portion. Accordingly, the above-described fast fill function is not deteriorated.
Further, the brake fluid supply from the large diameter pressurizing chamber to the small diameter hydraulic chamber at the initial stage of the operation can be carried out without by way of the reverse flow checking opening and closing portion and therefore, no fluid flow resistance is generated, and the fast fill function is further promoted.
In this way, since the ineffective stroke of the stepped piston until the cut-off portion on the small diameter hydraulic chamber side is brought into the closed state and is made longer than the ineffective stroke of the stepped piston until the cut-off portion on the large diameter pressurizing chamber side is brought into the closed state, in shortening the ineffective stroke for realizing the fast fill function at an early stage, the master cylinder is required to control the positional accuracy only of the cut-off portion on the large diameter pressurizing chamber side in the axial direction, and it is not necessary to strictly control positional accuracy in the axial direction of the cut-off portion on the small diameter hydraulic chamber side.
Therefore, the cut-off portion on the large diameter pressurizing chamber side can be constituted in correspondence with high flow, to have a short ineffective stroke and to satisfy fast fill, and the cut-off portion on the small diameter hydraulic chamber side can be constituted to be of a low cost type in correspondence with high flow and having the long ineffective stroke.